The present invention relates to solenoid actuated directional valves and is particularly concerned with an improvement for readily converting valves for use with either 50 hertz or 60 hertz alternating current without the necessity of either re-wiring or replacing the solenoids.
Solenoid actuated valves, such as hydraulic directional valves, are used in fluid power systems to control the flow of pressure fluid to components of the fluid power system. The directional valve comprises a valve body having a central bore having axially spaced annuli and within which a landed valve spool is disposed. The spool is shifted axially of the bore to selectively connect selected ports of the valve so that flow in the fluid circuit containing the valve is thereby controlled. In a solenoid actuated valve the valve spool is shifted within the bore by operation of one or more solenoids.
In the United States where 115 volt, 60 hertz, AC power is generally available the valve solenoids are designed to operate with maximum efficiency at that electrical voltage and frequency. While a solenoid may be capable of operating at actual line voltages and frequencies which depart from the nominal design values, the operating characteristics increasingly depart from optimum as the electrical power characteristics increasingly depart from their nominal values. For example, if the power frequency decreases from the nominal 60 hertz value, the inductive reactance of the solenoid coil similarly decreases because the inductive reactance is directly proportional to the line frequency. Consequently the current draw by the solenoid coil increases which itself gives rise to increased power consumption appearing as increased heat in the solenoid winding. Apart from the inefficient use of the electrical power, heat can have a deteriorating effect on the solenoid if it becomes too severe. Correspondingly, where the frequency of the power supply increases, the solenoids do not operate as well at the higher frequency because of reduced current draw and a resultant reduction in effective operating force.
Not all sites where directional control valves are used have 60 hertz electrical power available. For example in many areas of the world other than 60 hertz power is the rule. A typical figure in certain countries is 50 hertz power. The application of 50 hertz power to a solenoid coil which is designed for 60 hertz power, and vice versa, can have undesiable consequences, chiefly for the reasons explained above. Where an existing machine or piece of equipment which includes solenoid operated valves is to be relocated from one installation site to another where the electrical power supplied at the respective locations are at different frequencies, it has heretofore often been necessary to replace the solenoids with the new solenoids which are compatible with the new electrical power supply characteristics. Needless to say, the task of replacing the solenoids is a significant inconvenience. It involves the use of electricians who remove the old solenoid coils by disconnecting electrical lead wires of the solenoids from terminal blocks on the valve bodies. The new solenoids are installed and their lead wires are connected to the terminal blocks. Thus the total cost involved includes both the cost of new replacement solenoids and the labor cost in replacing the solenoids as well.
Even if a solenoid is manufactured with a tap allowing use with either 50 hertz or 60 hertz power, it is still necessary to rewire the solenoid leads on the terminal block whenever the valve is converted for use at a new frequency. If a compromise design is used so that replacement and rewiring are not required (for example say a 55 hertz design), actual operation (i.e. at either 50 hertz or 60 hertz) is never optimum.
The present invention is directed to a improvement in a solenoid operated directional valve whereby it is unnecessary to replace the solenoid assembly when the frequency of the electrical power supply changes from one frequency to another. Furthermore, the procedure involved in converting the solenoid for its new use can be done without the need to rewire the lead wires of the solenoid on the terminal blocks, and this results in a savings in labor cost in the changeover of a solenoid. The invention also provides improvement in other respects.
Where a manufacturer manufactures a range of different sized valves there are often various valve models which can use the same solenoid insofar as the electrical characteristics of the solenoid are concerned. This is particularly the case for valves having plug-in type solenoids such as disclosed in the commonly assigned prior patent application Ser. No. 241,355 filed Mar. 6, 1981. The dimensions of the valve bodies of the respective models may however be slightly different so that when a given solenoid design is suitable for use with two different valve bodies there may be some type of an adapter between the solenoid and one or more of the valve bodies whereby the solenoid is rendered compatable with all valve bodies. The present invention allows a solenoid to be capatible with many different valve bodies thereby eliminating use separate adapter elements.
Briefly a valve of the present invention has a connector element for switching between 50 and 60 cycle operation, and it can be configured to inherently incorporate the adapter function where an adapter would otherwise be required. Hence the advantage of this aspect of the invention is that a greater commonality of component parts is possible thereby minimizing manufacturing considerations and inventory requirements. The invention, in its disclosed preferred embodiment, allows a solenoid to be changed from 50 hertz to 60 hertz operation simply by disassembling the solenoid assembly from the valve assembly, repositioning the connector element on the solenoid assembly, and then reassembling the solenoid assembly to the valve assembly. There is no need to unfasten or refasten lead wires from or to terminal blocks. Furthermore because there are no lead wires on the solenoid assembly it is less susceptible to damage than other types of solenoids having lead wires where the lead wires may be grabbed to carry the solenoid.
Further advantages, features and benefits of the invention, along with the above, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.